The Reagan administration, concerned about possible Soviet violations of strategic nuclear arms agreements, has called for a special session of the U.S.-Soviet Standing Consultative Commission that was set up in 1972 to monitor adherence to such agreements.

Secretary of State George P. Shultz relayed the administration's request to the Soviets last month. Moscow, however, has not responded or agreed to a special session, according to administration officials. The SCC meets regularly twice a year and and can hold additional special sessions.

American officials said yesterday that discussion of these issues might also come through other channels and contacts with the Kremlin.

At the time of the U.S. request in July, officials said the main concern was the testing, which began in February, of a Soviet intercontinental-range missile of a type that may not be allowed under past agreements.

The Soviets also were encoding electronic signals the missiles were transmitting during the tests to prevent the United States from learning much about the weapon. U.S. officials say they believe the extent of this encryption may violate arms agreements.

Since then, Washington also has become concerned about a large Soviet radar, recently spotted by U.S. spy satellites, that intelligence reports suggest may be a violation of the 1972 Anti-Ballistic Missile (ABM) treaty, which limits the kind and location of radars in such defense systems.

Officials here say that, at the moment, the continued testing of the new Soviet missile, known as the PL5, remains the main focus of U.S. concern but that discussion of the new radar and other issues is also likely to come up if a special session is scheduled.

There has been concern for years--especially among a small group of conservative arms officials, lawmakers and some of their aides--about a long list of alleged Soviet violations of the 1972 SALT I strategic arms agreement, ABM treaty and the 1979 SALT II accord, which the United States did not ratify.

Until now, however, the United States has refrained from charging Moscow with any violation, in part because the agreements are vague. But there is a growing opinion, even among many moderates in the arms control field, that some of Moscow's latest activity may well violate one or more of these agreements.

The Soviets have already stated they are testing one large new missile, the SSX24.

The testing of the PL5 has been known publicly for several months. At issue is whether this is a new missile or, as Moscow claims, a version of the older SS13 missile that has been modified within the improvements agreements allow.

Recent U.S. analysis of PL5 tests suggests that the missile and its warhead are much larger than a modified SS13. This would make it a second "new" missile and therefore a violation of SALT II, which allows each side just one new missile. Some specialists, however, say the Soviets cannot be charged with a violation until they exceed the number of tests allowed.

The radar discovery is new, reportedly spotted only last month. The initial public account of the radar sighting was reported in considerable detail on July 27 by Roland Evans and Robert Novak in a syndicated column that appeared in a number of newspapers, including The Chicago Sun-Times.

Officials have confirmed the columnists' account. The new radar is reportedly located well inland in Siberia near Abalakovo, about 500 miles north of the Mongolian border.

Under the ABM treaty, radars built to warn of an enemy attack must be located along the borders of a country. Putting this big radar inland raises suspicions that it may be meant to operate in conjunction with the interceptor missiles of an anti-missile defense system.